# 矢量瓦片相关计算函数

Fiya_Z

import turf from 'turf'
export default {
TILE_SIZE: 256,
/*
* 获取指定级别的瓦片数目
*/
_getMapSize(level) {
return Math.pow(2, level);
},
/**
* Convert a longitude coordinate (in degrees) to the tile X number at a
* certain zoom level.经度转瓦片列号
* @param longitude
*            the longitude coordinate that should be converted.
* @param zoom
*            the zoom level at which the coordinate should be converted.
* @return the tile X number of the longitude value.
*/
longitudeToTileX(longitude, zoom) {
let px = this.longitudeToPixelX(longitude, zoom);
return this.pixelXToTileX(px, zoom);
},
/**
* Convert a latitude coordinate (in degrees) to a tile Y number at a
* certain zoom level.纬度转瓦片行号
* @param latitude
*            the latitude coordinate that should be converted.
* @param zoom
*            the zoom level at which the coordinate should be converted.
* @return the tile Y number of the latitude value.
*/
latitudeToTileY(latitude, zoom) {
let py = this.latitudeToPixelY(latitude, zoom);
return this.pixelYToTileY(py, zoom);
},
/**
* Convert a latitude coordinate (in degrees) to a pixel Y coordinate at a
* certain zoom level.经纬度坐标(纬度)转屏幕像素坐标(Y)
*
* @param latitude
*            the latitude coordinate that should be converted.
* @param zoom
*            the zoom level at which the coordinate should be converted.
* @return the pixel Y coordinate of the latitude value.
*/
latitudeToPixelY(latitude, zoom) {
let sinLatitude = Math.sin(latitude * Math.PI / 180);
return (0.5 - Math.log((1 + sinLatitude) / (1 - sinLatitude)) / (4 * Math.PI)) * (this.TILE_SIZE << zoom);
},
/**
* Convert a longitude coordinate (in degrees) to a pixel X coordinate at a
* certain zoom level.经纬度坐标(经度)转屏幕像素坐标(X)
*
* @param longitude
*            the longitude coordinate that should be converted.
* @param zoom
*            the zoom level at which the coordinate should be converted.
* @return the pixel X coordinate of the longitude value.
*/
longitudeToPixelX(longitude, zoom) {
return (longitude + 180) / 360 * (this.TILE_SIZE << zoom);
},
/*
* 指定级别下，将宏观上的经度转换为对应列上的瓦片的像素矩阵列号(微观)
例如：鼠标点击地图，鼠标位置在点击的瓦片内的行列号(即使像素行列号)。根据该瓦片(png)和计算出的行列号，即可取得鼠标点击位置的像素值。
*/
_lngToPixelX(longitude, level) {
let x = (longitude + 180) / 360;
let pixelX = Math.floor(x * this._getMapSize(level) * 256 % 256);
return pixelX;
},
/*
* 指定级别纬度对应的像素行号
*/
_latToPixelY(latitude, level) {
let sinLatitude = Math.sin(latitude * Math.PI / 180);
let y = 0.5 - Math.log((1 + sinLatitude) / (1 - sinLatitude)) / (4 * Math.PI);
let pixelY = Math.floor(y * this._getMapSize(level) * 256 % 256);
return pixelY;
},
/**
* Convert a pixel X coordinate to the tile X number.
* 像素坐标X转瓦片行列号X
* @param pixelX
*            the pixel X coordinate that should be converted.
* @param zoom
*            the zoom level at which the coordinate should be converted.
* @return the tile X number.
*/
pixelXToTileX(pixelX, zoom) {
return Math.floor(Math.min(Math.max(pixelX / this.TILE_SIZE, 0), Math.pow(2, zoom) - 1));
},
/**
* Converts a pixel Y coordinate to the tile Y number.
* 像素坐标Y转瓦片行列号Y
* @param pixelY
*            the pixel Y coordinate that should be converted.
* @param zoom
*            the zoom level at which the coordinate should be converted.
* @return the tile Y number.
*/
pixelYToTileY(pixelY, zoom) {
return Math.floor(Math.min(Math.max(pixelY / this.TILE_SIZE, 0), Math.pow(2, zoom) - 1));
},
}

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